Vacuum degasser



Aug. 22, 1967 J. A. SNYDER VACUUM DEGASSER 2 Sheets-Sheet 1 Filed Aug.28, 1964 FIG. 1

INVENYLOR. John A. Snyder ATTORNEY Aug. 22, 1967 Filed Aug. 28, 1964FIG.2

O 0 55: O O

35A no.4

J. A. SNYDER VACUUM DEGASSER 2 Sheets-Sheet 2 &

United States Patent tion of New Jersey Filed Aug. 28, 1964, Ser. No.392,801 3 Claims. (Cl. 266-13) The present invention relates generallyto the production of high purity steel, and more particularly to animproved apparatus for purifying steel by the vacuum degassing method.

In order to meet the modern specification requirements for steelproducts, such as bearing parts, that are to be used to near the limitof their physical characteristics, it is necessary that the steel fromwhich these products are made be as pure and free from solid or gaseousinclusions as possible. Vacuum degassing is a process used between themelting and ingot pouring steps in the steel making process to removegaseous materials, particularly oxygen, hydrogen, nitrogen and theircompounds, from the molten steel. In vacuum degassing, the free surfaceof the molten steel contained in a vessel is subjected to a high vacuum,i.e., less than an absolute pressure of 100 microns of mercury, and thebody of molten metal is then stirred or otherwise agitated to expose theentire mass of metal to the free surface whereby the gases included inthe metal are drawn from the free surface due to the difference betweentheir pressure and that of the vacuum. It will of course be recognizedthat the vacuum degassing of large masses of molten metal, e.g. batchesof 50 tons or more, at commercial rates requires the use of extremelylarge and expensive equipment.

The large vacuum degassers built prior to the arrangement of the presentinvention employed a pit-type chamber having a removable top cover. Theladle or vessel containing the molten steel to be degassed was firstlowered into the chamber by means of a crane. Then the top cover wasplaced in position, and the vacuum applied to the chamber. Suitablemeans, such as an induction stirring device, were permanently mountedwithin the chamber for agitating the mass of metal to expose it to thevacuum conditions maintained within the chamber. After the desireddegree of degassing'was accomplished, the chamber top cover was removedand the ladle lifted out of the chamber by the crane and removed to theingot pouring area.

Although this arrangement proved to be satisfactory insofar asaccomplishing the desired degree of degassing was concerned, the expenseof the equipment and the chiciency with which it could 'be utilized werefound to be considerably less than ideal. Since the degassing operationis accomplished between the melting and ingot pouring stages ofproduction, it is absolutely essential that a minimum amount of time beused in performing the degassing operation so that the heat loss andtemperature decline of the molten metal may be kept to a minimum.Because of the handling problems associated with pit-type degassers, thetime consumed in degassing was marginally close to the allowable limit.Moreover, the handling procedures employed were not readily adaptable tothe flow-through production methods of modern steel mills.

Since the present steel producing capacity in the United States isconsiderably greater than the market demand, very few new steel millsare being erected. Vacuum degassers, a relatively recent innovation, aretherefore usually incorporated into an existing steel making plant orfacility. Although high capacity cranes are a normal part of theequipment in a steel melting and pouring plant, when considering thelarge size of a vacuum degasser installation, there is rarely availablespace in which the chamber can be located in an existing facility withcomplete access to a crane of suflicient capacity. Thus, in inicestances where a pit-type or top loading degasser is to be installed, thedegasser installation almost invariably necessitates the concurrentinstallation of a degasserservice crane, the initial cost of which isabout 15% of the cost of the degasser itself.

Thus, it can be seen that the pit-type of degassing chamber has apparentshortcomings making its incorporation into the usual steel millproduction scheme both awkward and expensive.

It is therefore an object of the present invention to provide a vacuumdegassing apparatus which may readily be incorporated into theflow-through production schemes of a modern steel mill. It is a furtherobject to provide a vacuum degasser arrangement which may be installedintegrally into an existing steel melting and pouring facility whilerequiring a mini-mum amount of space, outlay of capital and disturbancesof the normal production arrangement. It is a still further object ofthe present invention to provide a vacuum degasser chamber arrangementin which the complete degassing operation may be accomplished with aminimum amount of material handling in a lesser amount of time than hasheretofore been possible.

To accomplish these objects, according to the present invention there isprovided an apparatus for degassing a body of molten metal contained ina large ladle and having a free liquid surface, which apparatus includesupright side walls and a roof defining an enclosed degassing chamber.The chamber walls are provided with a side opening through which theladle, carried on a wheeled carriage, may be admitted into the chamber,and a slidably movable door is arranged to cover and seal the door ingas tight relationship to the boundaries of the opening during thedegassing operation. Pump means, such as a jet injector system, areconnected with the chamber for evacuating substantially all theatmosphere from the chamber to form and maintain a vacuum therein.Tracks on which the carriage is adapted to move extend between the steelmelting and steel pouring facilities and into and outwardly from thechamber through the opening formed in the chamber walls. A detachableprime mover, which is located outside the chamber when the door isclosed, is provided for moving the carriage along the tracks into andout of the chamber. An induction stirring device, powered through adetachable connector located within the chamber, is permanently mountedon the carriage and is constructed and arranged to circulate'the metalwithin the carriage with a horizontal and vertical component of movementso that substantially all the metal is exposed at the liquid surface tothe vacuum conditions within the chamber during the degassing operation.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawing and descriptivematter in which there is illustrated and described a preferredembodiment of the invention.

In the drawings:

FIG. 1 is a perspective view of a vacuum degassing apparatus accordingto the present invention;

FIG. 2 is a floor plan showing the incorporation of the vacuum degasserof FIG. 1 into a steel melting and pouring plant;

FIG. 3 is a side elevation view of a movable track section at theentrance and exit of the degassing chamber;

FIG. 4 is a sectional end elevation taken along line 4-4 of FIG. 3; and

FIG. 5 is a sectional view showing the door seal arrangement taken alongline 5-5 of FIG. 1 when the door is closed.

Referring to FIG. 1, the degassing chamber 16 is formed of a roof 12 andside walls 14 which are reinforced with structural steel members 14A sothat the walls 14 can withstand the inward force of the atmosphere whenthe chamber is evacuated. The chamber walls are formed with opposedentrance and exit side openings or doorways which are sufficiently largeto pass the ladle carried on the transfer car or Wheeled carriage 25. Asshown in FIGS. 1 and 2, the carriage operates on rails 35 which extendthrough the doorways of the chamber 10. It should be recognized that thecarriage 25 may readily be pushed or pulled along the tracks 35 into,through and out of the chamber 10 by a suitable detachable prime movergenerally indicated at 24 in FIG. 2.

A air of covers or doors 16 (one of which is open and one of which isclosed in FIG. 1) are provided for purposes of closing the doorwaysduring the degassing operation, and are also suitably reinforced bystructural steel members 16A. The doors 16 are each hung by rollers 17which are arranged to roll along the channel shaped track 18 overlyingand extending laterally beyond the respective doorways. During thedegassing operation, the doors 16 are rolled into place over theirrespective doorways and are engaged in gas-tight sealing relationship tothe doorway boundaries by a sealing arrangement to be describedhereinafter.

A control room 50 is arranged atop and to the one side of the chamber10, the control room being thus disposed to afford an operator the bestpossible view of the overall operation. Roof sighting tubes 51 areprovided with transparent covers to allow viewing of the ladle 20 andthe metal contained therein when the doors 16 are closed. Additive bins52 disposed on the roof 12 of the chamber 10 are provided for purposesof adding pre-measured quantities of alloying materials to the metal inthe ladle 20 during the degassing operation.

The required vacuum (usually less than 100 microns of mercury) isimposed in the chamber 10 by pump means or multi-stage steam injectorjet system 301 which communicates via conduit 34 with the chamber 10through an opening 33 formed in one of the side walls 14. In FIG. 1, thefive serially arranged injector jets of the system are designated 30A,36B, 30C, 30D, and 30E in the order of their serial arrangement.Condensers 31A and 31B are respectively interposed between the third andfourth stage jets 30C and 30D, and between the fourth and fifth stagejets 30D and 30B.

FIG. 2 indicates that the vacuum degassing chamber 10 may beconveniently located between an existing melting area or bay 40, and oneor more melting furnaces 41 located therein, and a teeming bay orpouring area 45 in which a multiplicity of ingot molds 46 are located.The rails on which the ladle-bearing carriage 25 is arranged to operate,extend through the chamber 10 between the melting bay and the teemingbay 45, so that the carriage 25 is accessible to the ladle handlingcrane facilities (not shown) in each of the bays 40 and 45. Thus, it canbe seen that the installation of the vacuum degassing apparatus into anexisting plant as shown in FIG. 2 eliminates the necessity of addingcrane facilities for handling the ladle 20. Also it is obvious from FIG.2 that the vacuum degassing operation, which is performed between themelting and ingot pouring stages of production, can be accomplished inthe disclosed apparatus with a minimum of ladle handling and lost timebecause of the flow-through arrangement of the degasser chamber 10 andits relative location with respect to the melting and pouring areas 40and 45.

The carriage 25 has permanently mounted thereon a stirring device orinduction stirrer 26 for magnetically circulating the molten metalwithin the ladle 20 to effect exposure of substantially all the moltenmetal to the vacuum conditions existing at the free surface of themolten metal and to insure thorough mixing of any additives charged tothe ladle 20 via the bins 52 during the degassing operation. Theinduction stirrer 26 includes a series of vertically stacked separatelyoperable coils 26A each of which circumscribes the ladle 20 when it ispositioned on the carriage 25. The coils 26A may be of downwardlydiminishing diameter so that they generally conform to the slightlyinwardly tapering sides of the lower portion of the ladle 20. With thisarrangement of coils 26A, a horizontal component of circulation resultsfrom the normal operation of the individual coils; moreover, a verticalcomponent may be afforded the stirring action by sequentially firing orenergizing the individual coils 26A. The induction stirrer is poweredthrough a detachable electrical connection (not shown) located withinthe chamber 10.

The ladle 20, which is usually of about ton capacity, is preferably madeof a non-magnetic material such as stainless steel to avoid its becomingmagnetized due to the operation of the stirrer 26. Diametricallydisposed outwardly extending trunnions 21 are provided on the sides ofthe ladle 25 for crane handling, and positioning lugs 22 welded to theupper sides of the ladle 20, are arranged to engage with a matingsupport frame 29 on the carriage 25 to insure the proper positioning andsupport of the ladle 20 thereon. During the degassing operation, the topof the ladle is covered by a heat shield 27 having a reflectiverefractory inner surface to prevent the unnecessary loss of radiant heatfrom the free molten metal surface within the ladle 20. Charging holes28 are provided in the heat shield 27 so that the additive material maybe charged from the bins 52 to the ladle 20 during the degassingoperation.

In order to prevent the leakage of outside air into the chamber 10, itis necessary to provide a seal for the doors 16. The sealing problemcreated by the rails 35 is resolved by providing movable rail sections35A (to be described hereinafter) at the entrance and exit of thechamber 10. With the track sections 35A removed all four boundaries ofeach doorway are accessible for use as sealing surfaces. The doorsealing arrangement is shown in FIG. 5 in which 16 is representative ofa door and 14B represents a structural steel member forming one of theboundaries or sides of a doorway and having a sealing surface 14C thatis in a plane parallel with the plane of the door 16. Weldedperipherally around the door 16 in a common plane are a pair of spacedpipes or rigid tubular members 56. A sealing tube 57, made of a suitableresilient material such as rubber, is suitably affixed to the door 16between the pipes 56. The cross-sec tional area of the sealing tube 57is such that it substantially fills the space between the pipes 56 whencompressed by the door 16. In operation, when the jet injector system 30starts to pull a vacuum on the chamber 10, the door 16 is urged, bysuit-able means such as hydraulic cylinders 58, toward the sealingsurface to establish contact of the sealing tube57 with the doorwaysealing surface 140. Thereafter, the vacuum within the chamber 10 willcause the sealing tube 57 of the door 16 to remain firmly engaged withthe sealing surface 14C, thereby effecting a substantially gas-tightseal. The pipes 56, arranged as shown, prevent the sealing tube 57 fromlateral displacement and also provide a protection to the tube 57 fromany molten metal that may be splashed from the ladle 20 during thedegassing operation. m

As mentioned above, movable track sections 35A are provided immediatelyadjacent the doorways to the chamber 10 so that there are suitableparallel sealing surfaces around the entire peripheries of the doors 16and their respective doorways. As shown in FIGS. 3 and 4, movable tracksections 35A are connected by hold-down lugs 63 and supported on arectangular frame consisting of a pair of spaced I-beams 61 extendingparallel to the track sections 35A and another pair of spaced I-beams 62extending perpendicular to and having their ends connected with theI-beams 61. The rectangular frame thus formed is supported on four wheelassemblies 65 connected to the undersides of the I-beams 61 and arrangedto engage the inverted angle tracks 66 which are suitably anchored tothe foundation 67. The movable track sections 35A are urged into and outof position through a rod 70 which interconnects the I-beam 61 that isnearest the door 16 to the lower corner of the door 16. A springassembly 71 is attached to the rod 70 and serves to prevent thetransmission of shock forces between the door 16 and the wheeled frameto which the track sections 35A are attached. Since the track sections35A and the door 16 are substantially rigidly interconnected, means areprovided for adjusting the length of the rod 70 so that the lateralposition of the track sections 35A may be adjusted to be in alignmentwith the tracks 35 when the door 16 is in its fully opened position.Thus, it can be seen that when the doors 16 are opened, the tracksections 35A will be moved into alignment with the tracks 35A so thatthe carriage 25 may be moved into, through or out of the chamber 10.Conversely, when the doors 16 are closed, the track sections 35A aremoved laterally out of alignment with tracks 35 so that the doors 16 maybe engaged around their entire peripheries in sealing relationships withthe boundaries of the doorways as described above.

As shown in FIG. 3, the floor 13 of the chamber is supported from thefoundation 67 by a support beam system SQWhlCh also supports theportions of the rails 35 within the chamber 10. A refractory pan orreservoir 85 is built up between the tracks 35 Within the chamber 10 andserves to catch any molten metal which may leak from the ladle 20 whileit is in the chamber 10. Thus, if a minor leak does develop, the leakagemay be confined to the pan 85 until the ladle 20 can be removed from thechamber 10.

To further demonstrate the utility of the invention disclosed herein, acomplete degassing operation will be described. The molten metal to bedegassed is poured from the melting furnace 41 into the ladle 20 in thepouring bay 40. The crane in the pouring bay 40 is then used to positionthe ladle 20 on the carriage 25. After the heat shield 27 has beenplaced on top of the ladle 20, the carriage 25 is pulled by the primemover 24 along tracks 35 into the degassing chamber 10. The prime mover24 is then detached from the carriage 25 and moved out of the chamber10, and the power connection for the induction stirrer 26 is made withinthe chamber 10. The doors 16 are then closed, which closing action alsomoves the track sections 35A out of their normal position so that theperipheral sealing surfaces around the doors 16 may be aligned. Thedoors 16 are then urged into engagement with their respective seals andthe jet injector system 30 is activated to produce the desired level ofvacuum within the chamber 10. During the time when vacuum conditions aremaintained within the chamber 10, the induction stirrer 26 is operatedto effect circulation or agitation of the molten metal within the ladle20, and the desired additives may be added to the laddle 20 from theadditive bins 52. After degassing has been completed, the vacuum in thechamber 10 is reduced, and the doors 16 are opened, the opening of thedoors 16 serving additionally to reposition the movable track sections35A. Induction stirrer 26 is then disconnected from its power source,and the prime mover 24 is coupled with the carriage 25. The ladle 20 maythen be transferred to the pouring area 45 where, utilizing the cranefacilities of the pouring bay 45, the molten metal from the ladle 20 ispoured into the ingot molds 46.

From the above, it can be seen that the vacuum degasser arrangementdisclosed herein necessitates a minimum amount of ladle handling andtime and utilizes existing crane facilities to a maximum extent.

While in accordance with the provisions of the statutes there isillustrated and described herein a specific embodiment of the invention,those skilled in the art will understand that changes may be made in theform of the invention covered by the claims, and that certain featuresof the invention may sometimes be used to advantage without acorresponding use of the other features.

What is claimed is:

1. Apparatus for degassing molten metal comprising, upright side wallsand a permanently afiixed roof defining an enclosed degassing chamber,pump means connected with said chamber for evacuating substantially allof the atmosphere therefrom to form a vacuum therein, furnace meansspaced from said chamber, ingot casting means spaced from said chamber,a ladle, means for pouring molten metal from said furnace means intosaid ladle, means for pouring molten metal into said ingot casting meansfrom said ladle, a wheeled carriage, means for placing said ladle in andremoving the ladle from said carriage, means to form an opening in saidchamber side wall sufficiently large so that said carriage holding saidladle can be passed through said opening, track means adapted for thetravel of said carriage thereon and extending from said furnace meansand said ingot casting means and into said chamber through said opening,an induction stirrer permanently mounted on said carriage andconstructed and arranged to circulate said metal within said ladlewhereby the metal is exposed to the vacuum within said chamber to effectdegassing, a detachable connector within said chamber for energizingsaid induction stirrer, a movable door arranged to cover said opening,movable track sections connected to and operable with said door to movesaid sections out of normal track alignment when closing said door,means for moving said carriage along said track means into and out ofsaid chamber, and means for engaging said door in gas-tight sealingrelationship to the boundaries of said opening.

2. Apparatus according to claim 1 including means to form openings inopposite upright walls of said chamber, track means which extend throughsaid chamber and opening means for movement of said carriage throughsaid chamber, and a movable door for each of said openings.

3. Apparatus according to claim 2 including means which define areservoir between the tracks within said chamber for catching any metalleakage from said ladle within said chamber.

References Cited UNITED STATES PATENTS 3,255,897 6/1966 Lacy 214 18FOREIGN PATENTS 866,928 5/1961 Great Britain.

OTHER REFERENCES High Vacuum Degassing Wit-h Induction Stirring MakesCleaner Steels, by Thomas E. Perry, vol. 83, Metal Progress, pp. 88-91,August 1963.

JOHN F. CAMPBELL, Primary Eaxminer.

R. F. DROPKIN, Assistant Examiner.

1. APPARATUS FOR DEGASSING MOLTEN METAL COMPRISING, UPRIGHT SIDE WALLSAND A PERMANENTLY AFFIXED ROOF DEFINING AN ENCLOSED DEGASSING CHAMBER,PUMP MEANS CONNECTED WITH SAID CHAMBER FOR EVACUATING SUBSTANTIALLY ALLOF THE ATMOSPHERE THEREFROM TO FORM A VACUUM THEREIN, FURNACE MEANSSPACED FROM SAID CHAMBER, INGOT CASTING MEANS SPACED FROM SAID CHAMBER,A LADLE, MEANS FOR POURING MOLTEN METAL FROM SAID FURNACE MEANS INTOSAID LADLE, MEANS FOR POURING MOLTEN METAL INTO SAID INGOT CASTING MEANSFROM SAID LADLE, A WHEELED CARRIAGE, MEANS FOR PLACING SAID LADLE IN ANDREMOVING THE LADLE FROM SAID CARRIAGE, MEANS TO FORM AN OPENING IN SAIDCHAMBER SIDE WALL SUFFICIENTLY LARGE SO THAT SAID CARRIAGE HOLDING SAIDLADLE CAN BE PASSED THROUGH SAID OPENING, TRACK MEANS ADAPTED FOR THETRAVEL OF SAID CARRIAGE THEREON AND EXTENDING FROM SAID FURNACE MEANSAND SAID INGOT CASTING MEANS AND INTO SAID CHAMBER THROUGH SAID OPENING,AN INDUCTION STIRRER PERMANENTLY MOUNTED ON SAID CARRIAGE ANDCONSTRUCTED AND ARRANGED TO CIRCULATE SAID METAL WITHIN SAID LADLEWHEREBY THE METAL IS EXPOSED TO THE VACUUM WITHIN SAID CHAMBER TO EFFECTDEGASSING, A DETACHABLE CON-